1. Field of the Invention
The invention relates to a matched seal feedthrough for glass-to-metal applications.
2. Description of the Related Art
On feedthroughs one generally distinguishes between “matched seal feedthroughs” where the coefficients of expansion of the material of the support body and the fixing material through which the functional element or elements, for example the contact pins, are guided are substantially the same; and so-called “compression seals” where the coefficients of thermal expansion of the fixing material are different to the coefficients of thermal expansion of the support body, so that a concentric compression load occurs on the glass. Compression seals are used primarily in the field of feedthroughs for airbag ignitors, as disclosed for example in EP 1 455 160. In a matched seal feedthrough where the coefficient of thermal expansion of the support body as well as that of the fixing material is substantially the same, the problem arises in that a hermeticity of the feedthrough must be produced, since this does not occur automatically as it does with a non-matched seal feedthrough, due to the compression pressure.
In the current state of the art a connection between the metal and the glass is made possible, for example by means of a metal oxide bridge, wherein the metal oxide has a coefficient of expansion that is substantially consistent with the longitudinal expansion of the fixing material.
For this purpose, nickel-iron or nickel-iron-cobalt alloys, for example “KOVAR®” are used in the current state of the art. Use of such nickel-iron or nickel-iron-cobalt alloys, however, has the disadvantage that these alloys do not have sufficient corrosion resistance. In one further advanced design variation, the state of the art provided that the region of the functional elements that was not glazed into the fixing material was provided with a surface coating, mostly a nickel plating. However, with this type of arrangement cracks occurred in the transition area between fixing material and functional element. These do not represent a problem for gas tightness and the electrical insulation resistance since they occur to a limited extent locally, but do however for the corrosion resistance of the components, since in the region of the cracks, areas of the functional elements emerge which are not protected by a surface coating. Thus, undesired corrosion can occur on the functional elements in the region of the cracks which can result in the contact pin breaking off.
A corrosion-resistant matched seal feedthrough is described in EP 0157685 A1. In the system according to EP 0157685 A1 the previously described problem of corrosion in the region of the cracks is also described. To avoid cracks of this type, EP 0157685 A1 provides use of a functional element from the inside to the outside of the feedthrough, consisting of a bimetal instead of a functional element consisting of a single metal, wherein the part of the contact pin protruding toward the outside is manufactured from a conducting corrosion-resistant material, and the part of the functional element facing toward the inside only needs to provide the electric conductivity and mechanical rigidity. With the system according to EP 0157685 A1 it was disadvantageous that the use of a bimetal for the functional element, in particular the contact pin, consisting of different materials requires high production costs. An additional disadvantage is that the transition of the two materials is not always completely smooth and free of imperfections, which additionally favors gas pockets in the glazing.
A matched seal feedthrough is known from EP 0157 685 A1, comprising a support body with at least one passage opening, as well as a functional element with an outside circumferential surface. The functional element is held in the passage opening by a fixing material, in particular a glass material. In order to prevent corrosion, it is suggested in EP 0157 685 A1 to design the functional element, in particular the contact pin as a bimetal conductor, in other words as a conductor consisting of two different metals. A coating of a conductor for corrosion prevention is not shown in EP 0157 685 A1.
DE 103 48 943 A1 describes a hermetically sealed electric feedthrough device with a pin glazed into a fixing material. However, the feedthrough in DE 103 48 943 A1 is not a matched seal feedthrough. Coating of a conductor is also not described in DE 103 48 943 A1.
US 2003/0096162 A1 describes a feedthrough for lithium ion batteries. The glass material that is used as fixing material is a CaO—Al2O3—MgO—B2O3 or respectively a CaO—Al2O3—B2O3 system that has a thermal expansion that extensively coincides with the thermal expansion of the glazed metal pin, in the current example a molybdenum pin. The metal pins in US 2003/0096162 A1 are coated, however over the entire length of the glazed pin. Cited coating materials are platinum, platinum-iridium, platinum alloys, materials similar to platinum such as titanium, aluminum, platinum-aluminum, iridium, rhenium, ruthenium, osmium, palladium, niobium, chromium, tantalum or combinations of the aforementioned metals or their oxides. The coatings serve to better join the metal pin with the surrounding fixing material, wherein a chemical bond is formed between the fixing material and the metal pin. Corrosion resistance is not achieved by the coating, rather the selection of the glass types provides corrosion resistance.
US 2004/0101746 A1 describes a glass feedthrough wherein the Kovar conductor comprises at least a partial coating on the outside circumference. Only the top and bottom part of the conductor is provided with a coating in US 2004/0101746 A1. The middle section is not coated.
No Kovar conductor is shown in US 2004/0101746 A1 where a nickel coating is in contact with the fixing material. The nickel layer in US 2004/0101746 A1 is a bonding agent under a gold plating, so that contact exists between the fixing material and gold, but not between the fixing material and nickel. An anti-corrosive effect of the nickel layer is not described in US 2004/0101746 A1. The nickel layer herein serves only as a bonding agent.
What is needed in the art is a matched seal feedthrough which avoids the aforementioned disadvantages of the current state of the art. In particular, a corrosion resistant matched seal feedthrough is needed that distinguishes itself through low production costs.